Sizes of Ballast
Previously, 50-mm (2") ballasts were specified for flat bottom sleepers such as concrete and wooden sleepers and 40-mm (1.5") ballasts were specified for metal sleepers such as CST-9 and trough sleepers. Now, to ensure uniformity, 50-mm (2") ballasts have been adopted universally for all type of sleepers.
As far as points and crossings are concerned, these are subjected to heavy blows of moving loads and are maintained to a higher degree of precision. A small sized, 25-mm (1") ballast is, therefore, preferable because of its fineness for slight adjustments, better compaction, and increased frictional area of the ballast.
Requirements of a Good Ballast
Ballast material should possess the following properties.
(a) It should be tough and wear resistant.
(b) It should be hard so that it does not get crushed under the moving loads.
(c) It should be generally cubical with sharp edges.
(d) It should be non-porous and should not absorb water.
(e) It should resist both attrition and abrasion.
(f) It should be durable and should not get pulverized or disintegrated under adverse weather conditions.
(g) It should allow for good drainage of water.
(h) It should be cheap and economical.